The Irish actor stars in the title role of the oddball comedy about the eccentric frontman of a pop band who hides his identity inside a Frank Sidebottom mask. Frank was the comedy alter-ego of London musician and comedian Chris Sievey, who performed wearing a large cartoon papier mache head.

Asked at the film's premiere in Dublin about performing with the giant head on, Michael said: "I just put the head on and the rest did itself.

"I wanted to really embody the character physically and there was a lot to do there. Sometimes with a head on that's animated, it's better to do smaller movements or no movements than be more expressive, funnily enough, and that just sort of happened through trial and error.

"But it was sort of freeing when you're wearing a mask like that. It's kind of fun."

The indie film - which also stars About Time's Domhnall Gleeson and Maggie Gyllenhaal and is directed by Irish filmmaker Lenny Abrahamson - is a comedy, but Michael insisted there are some serious themes at its heart.

He revealed the character of Frank is partly inspired by Daniel Johnston, an American musician who has been diagnosed with schizophrenia and manic depression.

Michael said: "He's weird and wonderful. He's an eccentric musical talent.There's elements of genius within there and also mental illness at the core of it, which we didn't want to be taken flippantly at all. He's a complex character. There's a lot of reference points that we took form Daniel Johnston."

Domhnall plays an aspiring young musician who joins Frank's band, dreaming of stardom.

Domhnall said of working with Michael: "He's an amazing actor and I think what's great, when people see the film, is that his performance comes through the mask when he wants it to. I think I learnt a lot, I hope I did, 'cause I'd be stupid if I didn't."